Technical Field
Exemplary embodiments of the present disclosure generally relate to an image projection apparatus.
Description of the Related Art
Image projection apparatuses such as projectors are widely known. Cost reduction of such image projection apparatuses is progressing due to recent advancements in resolution (i.e., higher resolution) of liquid crystal panels and recent advancements in brightness (i.e., improved brightness) of light sources (e.g., lamp) accompanying advancement in efficiency. Small and light-weight image projection apparatuses using a digital micro-mirror device (hereinafter referred to as DMD) are in widespread use in offices and schools. They are also becoming widely prevalent in homes.
With respect to such image projection apparatuses that project an enlarged projection image on a projection plane such as a screen using a projection lens, an intense light is outputted from a light emission portion of the image projection apparatuses. Looking into the light emission portion from the screen side is hazardous and may result in damaging one's eyes. Thus, warning labels and instructions, such as to prevent looking into the light emission portion, accompany the image projection apparatuses.
In a case in which an object (i.e., obstruction) such as a pocketbook or a document is placed in front of a light emission portion of an image projection apparatus with the objective of blocking emitted light, heat from emitted light accumulates between the obstruction and the image projection apparatus. Accordingly, excessive temperature rise of the image projection apparatus, particularly around a projection lens, occurs. Excessive temperature rise of the image projection apparatus may lead to malfunction of the image projection apparatus. In addition, the obstruction is also heated, sometimes to a dangerous degree. This excessive temperature rise and heating of the obstruction are thus undesirable.
An example of a conventional projector is shown in FIG. 14. In the example, malfunction due to an obstruction 94 is prevented by discharging air (i.e., air current 93) used to cool the inside of a projector body 90 from a side of the projector body 90 that includes a projection lens 91, and by controlling output of a lamp of the conventional projector based upon a detection value detected with a sensor 92. The sensor 92 detects changes in air pressure of the air current 93 influenced by the obstruction 94 placed in front of the projection lens 91.
However, changes in air pressure of the air current 93 are not only induced by the obstruction 94. Room environment in which the conventional projector is set also influences air pressure. Air pressure of the air current 93 detected by the sensor 92 changes from moment to moment. Thus, there is an issue of accuracy with respect to controlling output of the lamp based upon the air current 93 discharged from the conventional projector.
In a well-known conventional horizontal-type image projection apparatus, a projection lens is provided at a side surface of a housing of the conventional horizontal-type image projection apparatus. The conventional horizontal-type image projection apparatus is capable of projecting in a so-called “tilt projection” manner onto a screen. Thus, even if an obstruction such as a notebook or a pocketbook is placed in front of the projection lens, there is a space between the obstruction and the projection lens. Accordingly, the above-described excessive temperature rise does not easily occur with respect to the conventional horizontal-type image projection apparatus. Nevertheless, excessive temperature rise of the conventional horizontal-type image projection apparatus may occur depending on a distance between the obstruction and the projection lens.
By contrast, in an upright-type image projection apparatus, a projection unit that emits light from a projection lens is provided at an upper surface side of a housing of the upright-arranged image projection apparatus. To block emitted light, an obstruction such as a sheet or a stack paper must be placed on an upper surface of the housing. Thus, the obstruction easily adheres to the projection unit and there is no space in between the obstruction and the projection unit. Accordingly, heat from emitted light accumulates between the obstruction and the projection unit, and excessive temperature rise of the upright-type image projection apparatus easily occurs. In addition, the obstruction is heated. When space between the obstruction and the projection unit is insufficient as in the above-described upright-type image projection apparatus, adopting a configuration of the above-described conventional projector that detects air pressure is not possible.